In a magnetic disk drive, in general, dynamic flying height (DFH) control of raising a magnetic head to a flying height position for seek simultaneously with seek start and falling the magnetic head to a flying height position for read/write (hereinafter R/W) before seek completion is executed.
In the magnetic disk drive, control for media bump avoidance is executed together with DFH control. In this case, media bumps exist in the seek destination direction of the seek start track and, if the magnetic heads are expected to collide with the media bumps, control of delaying the seek start until the magnetic heads reaches the flying height position for seek is executed. In addition, media bumps exist in the seek source direction of the seek completion track and, if the magnetic heads are expected to collide with the media bumps, control of falling the magnetic heads after passing the media bumps is executed.
If the above-explained DFH control and control for media bump avoidance are executed, a latency caused by the media bump avoidance control is not considered, but the time obtained by summing a seek time determined from a seek distance and a rotational latency determined by a relationship between an R/W enable sector position and sector position of a command to be evaluated, after seek completion, is used and, if a command accessible in the shortest time is selected by the reordering, the seek is delayed due to the media bump avoidance, rotational latency occurs in a case where the seek is not completed before a start sector of a selected command, and the performance is degraded.
The object to be solved by the embodiments is to provide a magnetic disk drive and a magnetic head control method capable of reducing the rotational latency by considering the seek latency which occurs due to the media bump avoidance control executed together with the DFH control, at the reordering operation.